This application is based on application No. 2002-271783 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to a camera, such as a single-lens reflex camera employing a film and a single-lens reflex type of digital camera, having a control device for controlling flash photography in which there is provided a TTL (i.e. Through The Lens) focus detection device, and to a method for controlling the flash photography, and particularly relates to the camera which emits a preliminary flash light and controls the amount of emission of a main flash light on the basis of information obtained from the emission of the preliminary flash light, and to the method for controlling the flash photography.
2. Description of the Related Arts
As a method for controlling the amount of flash light emission of a camera, conventionally, there have been proposed a method of flashmatic control for controlling the amount of flash light emission, on the basis of a distance between the camera and an object (or subject) to be photographed and on the basis of the setup amount of aperture thereof, and a method of TTL direct light adjustment control for measuring the amount of light reflected from the surface of a film while exposing the film to light and for stopping the exposure of the film thereto when the amount of the light reaches a predetermined one thereof, or the like.
For example, U.S. Pat. No. 4760418 discloses a technique that the flux of light (i.e. beam of light or luminous flux) is measured by a focus detection sensor at time of flash light emission, and that the amount of the flash light emission is adjusted by detecting the output of the light amount integration (or integral) of the sensor. In the technique, the light reflected on the film surface is led to the sensor at time of the exposure of a film to light, and the flash light emission is stopped when the amount of the flash light emission reaches a predetermined one, by the TTL direct light adjustment control.
According to the technique, a focus detection sensor (hereinafter, also referred to as an xe2x80x9cAF sensorxe2x80x9d) which is employed for detecting focus condition is also employed as a light adjustment sensor for detecting the light which is reflected from the object (or subject) to be photographed. In other words, the operation of the light adjustment and that of the focus-detection, are performed by a single sensor. That is, not only the arrangement makes it possible to save a space for arranging the light adjustment sensor so that the camera is downsized, but also the lower cost of the camera is achieved by omitting the light adjustment sensor.
According to the technique, at the stage of performing the operation of the auto-focus, the light of the object to be photographed is reflected on the mirror, and the light thus reflected thereon can be led to the AF sensor. However, at the stage of photographing the object, it is necessary to retreat the mirror; namely, it is not possible to employ the mirror. Therefore, a particular means for leading, or guiding, the light of the object reflected on the film surface towards the AF sensor, is required (refer to FIGS. 1 and 2 in the same publication). That is, such an additional means complicates the mechanism around the mirror, and increases the number of parts constituting the whole mechanism. As a result, the size and cost of the camera increase.
Additionally, generally, the range from maximum to minimum signal levels that the monitor of the AF sensor can integrate is narrow so that it is difficult to employ the AF sensor also as the light adjustment sensor. That is, according to the arrangement, when the flash light emission is made, the output from the sensor is overflown because the amount of the reflected light is excessive, if the reflectance of an object to be photographed is greater and/or if the distance between the object and the camera is smaller. Or, sufficient output from the sensor can not be obtained since the amount of the reflected light is small, if the reflectance of an object to be photographed is smaller and/or if the distance between the object and the camera is greater. Namely, in each case, it is not possible to perform the light adjustment control with a high precision.
On the other hand, in a case that a light receiving element or component with a high performance, as an AF sensor, which has a wider range from maximum to minimum signal levels that the sensor can integrate, is employed, the cost of the camera having the mechanism is up.
Therefore, it is an object of the present invention to provide a low-cost camera having a simple mechanism, in which an AF sensor functions as a light adjustment sensor.
It is another object of the present invention to provide a method for controlling flash photography employed by the camera.
In accomplishing these and other objects of the present invention, according to one aspect thereof, there is provided a camera comprising: a multi-AF sensor having a plurality of detection areas for receiving a reflected light, passing through a photographing lens, from an object to be photographed, in which each of the detection areas outputs a signal; an AF controller for determining a detection area of the detection areas as a focus area on a basis of the signal outputted from the each of the detection areas of the multi-AF sensor; a selector for selecting a detection area of the detection areas as an optimum area which is most suitable for photographing the object, on a basis of the signal outputted from the each of the detection areas of the multi-AF sensor, in which the signal outputted from the each thereof corresponds to the reflected light from the object on a basis of a preliminary flash light emission made by a flash emitter prior to a main flash light emission made by the flash emitter; and a controller for determining an amount of flash light emission made by the flash emitter at time of the main flash light emission, on a basis of the signal outputted from the optimum area selected by the selector.
That is, according to the arrangement, the preliminary flash light is emitted firstly, and then the main flash light is emitted for exposure. In other words, by employing the AF sensor as the light adjustment sensor, it is possible to cancel a member for securing an optical path for guiding the light from the object to be photographed. Namely, with the arrangement, there is no need of a separate light adjustment sensor, thus realizing a low-cost camera having a simple mechanism.
Also, according to the arrangement, when the brightness of part of the object is high, and when the brightness thereof is beyond a certain limit within which the multi-AF sensor can integrate electrical charges, such a situation as it is impossible to control the light adjustment is avoided, and the amount of the main light emission is determined by selecting a particular area of the detection areas which outputs a suitable signal. That is, the range from maximum to minimum signal levels that the multi-AF sensor can integrate, is expanded substantially, by separately processing each of the signals having different values which are outputted from the plurality of the detection areas locating in a focussing area, so that the amount of the main flash light emission can be calculated.
In the arrangement, in a case that the camera is of a type of single-lens reflex digital camera, it is possible to execute a TTL (through-the-lens (metering)) light adjustment even if the image sensor, of the camera, for photographing an object, does not have a flash light monitoring function.